Firmware is the read-only-memory (ROM)-based software that controls a computer between the time it is turned on and the time the primary operating system takes control of the machine. Open Firmware provides the following: a mechanism for loading and executing programs (such as operating systems) from disks, tapes, network interfaces, and other devices; an ISA-independent method for identifying devices "plugged in" to expansion buses and for providing firmware and diagnostics drivers for these devices; an extensible and programmable command language based on the Forth programming language; methods for managing user-configurable options stored in nonvolatile memory; a "call back" interface allowing other programs to make use of Open Firmware services; and debugging tools for hardware, firmware, firmware drivers, and system software.